1. Field of the Invention
The present invention relates to a method and an apparatus for detecting the shape of flat products such as strip or sheet from tension distributions along the widths of the products.
2. Description of the Prior Art
Generally in cold-rolling operations for making flat products such as steel strip, exactness in shape (or "flatness") of such products, as well as that in thickness, is the key factor to the success of the operations. In fact, the cold-rolling mill operates at high tension, and if there are regions of irregularity such as center buckles or edge waves due to elastic elongation with a product, the irregular part of the shape caused by these irregular regions may be affected or even offset by such high tension, making it possible to detect the irregular shape directly by using the regions of irregularity as determinative factor.
As a means for indirectly detecting the shape of flat products, the tension distribution on flat products in the width direction heretofore been used. This idea is sound, since the fact is that the shape of flat products can be measured on the basis of the difference in length with respect to points taken along the width of the flat products, such difference causing a varied tension distribution on the flat product in response to the application of tension thereon. This makes it possible to detect the irregular part of the shape of the flat product indirectly, that is, in view of such tension distribution. Again, this method is possible because of the close relationship between the shape of flat products and the tension distribution thereon in the width direction.
The known methods of detecting the tension distribution for this purpose include a method using strain guages for a plurality of detection rolls provided separately in the width direction of flat products and a method utilizing magnetic strain. However, detection using these methods results in substantial errors caused by, for example heaving of the examined material. Moreover the number of detection elements which can be used is limited to several because of the structure of the setting device. Since their tension resolution in the width direction is low, the data obtained by using these methods is inaccurate. Because of the abovementioned and other disadvantages, these methods are still untrustworthy in the detection of tension distribution.